Multilayer dental appliances and related methods and systems

ABSTRACT

A dental appliance for positioning a patient&#39;s teeth includes a removable orthodontic tooth positioning appliance having teeth receiving cavities shaped to directly receive at least some of the patient&#39;s teeth and apply a resilient positioning force to the patient&#39;s teeth. The appliance includes a hard polymer layer having a hard polymer layer elastic modulus disposed between a first soft polymer layer having a first soft polymer layer elastic modulus and a second soft polymer layer having a second soft polymer layer elastic modulus. The hard polymer layer elastic modulus is greater than each of the first soft polymer layer elastic modulus and the second soft polymer layer elastic modulus. At least one of the first soft polymer layer and the second soft polymer layer has a flexural modulus of greater than about 35,000 psi.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/043,065, filed Jul. 23, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/476,622, filed Mar. 31, 2017, now U.S. Pat. No.10,052,176, issued Aug. 21, 2018, which is a continuation of U.S. patentapplication Ser. No. 13/470,681, filed May 14, 2012, now U.S. Pat. No.9,655,691, issued May 23, 2017, the entire contents of each areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to the field of orthodontics,and more particularly to the design of multilayer dental positioningappliances.

An objective of orthodontics is to move a patient's teeth to positionswhere function and/or aesthetics are optimized. Traditionally,appliances such as braces are applied to a patient's teeth by a treatingpractitioner and the set of braces exerts continual force on the teethand gradually urges them toward their intended positions. Over time andwith a series of clinical visits and reactive adjustments to the bracesby the practitioner, the appliances to move the teeth toward their finaldestination.

More recently, alternatives to conventional orthodontic treatment withtraditional affixed appliances (e.g., braces) have become available. Forexample, systems including a series of preformed appliances/alignershave become commercially available from Align Technology, Inc., SanJose, Calif., under the trade name Invisalign® System. The Invisalign®System is described in numerous patents and patent applications assignedto Align Technology, Inc. including, for example in U.S. Pat. Nos.6,450,807, and 5,975,893, as well as on the company's website, which isaccessible on the World Wide Web (see, e.g., the url invisalign.com”).The Invisalign® System includes designing and/or fabricating multiple,and sometimes all, of the aligners to be worn by the patient before thealigners are administered to the patient and used to reposition theteeth (e.g., at the outset of treatment). Often, designing and planninga customized treatment for a patient makes use of computer-based3-dimensional planning/design tools, such as Treat™ software from AlignTechnology, Inc. The design of the aligners relies on computer modelingof the patient's teeth in a series of planned successive tootharrangements, and the individual aligners are designed to be worn overthe teeth, such that each aligner exerts force on the teeth andelastically repositions the teeth to each of the planned tootharrangements.

While recently developed orthodontic treatment technologies, such asthose described above, represent a considerable advancement in the fieldof orthodontics, additional advancements remain of interest. Forexample, in some instances it may be advantageous to develop materialsthat improve properties of the appliances/aligners used for orthodontictreatment. As such, there is a need for shell aligners that can, forexample, produce more continuous force and better bring a patient'steeth into a desired occlusion.

BRIEF SUMMARY OF THE INVENTION

The present invention provides multilayer orthodontic positioningappliances, as well as related methods and systems. The disclosedmultilayer appliances include a removable orthodontic tooth positioningappliance having teeth receiving cavities shaped to directly receive atleast some of the patient's teeth and apply a resilient positioningforce to the patient's teeth. The multilayer appliances can include ahard polymer layer disposed between two soft polymer layers. Themultilayer dental appliances of the present invention, among manyaspects, provide, for example, improved material performance, stressrelaxation properties and longer working range. In addition, themechanical properties of the materials and appliances described hereincan improve orthodontic treatments by, for example, reducing the needfor midcourse corrections during treatment and the number of alignersused for a given treatment.

The disclosed methods include methods for making multilayer dentalappliances. The disclosed systems including a plurality of applianceshaving teeth receiving cavities shaped to directly receive at least someof the patient's teeth and apply a resilient positioning force to thepatient's teeth. The appliances can be successively worn by a patient tomove teeth from one arrangement to a successive arrangement. At leastone of the appliances in the system can include a hard polymer layerdisposed between two soft polymer layers.

For a fuller understanding of the nature and advantages of the presentinvention, reference should be made to the ensuing detailed descriptionand accompanying drawings. Other aspects, objects and advantages of theinvention will be apparent from the drawings and detailed descriptionthat follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a jaw and an incremental positioning appliance forthe jaw, in accordance with an embodiment of the present invention.

FIG. 2 shows an arrangement of polymer layers in a sheet having a hardpolymer layer disposed between two soft polymer layers, in accordancewith an embodiment of the present invention.

FIG. 3 depicts a method of making a multilayer dental appliance, inaccordance with an embodiment of the present invention.

FIG. 4 is a simplified block diagram illustrating a method forfabricating a dental appliance, in accordance with an embodiment of thepresent invention.

FIG. 5 provides a stress relaxation comparison for dental appliances, inaccordance with an embodiment of the present invention.

FIG. 6 provides another stress relaxation comparison for dentalappliances, in accordance with an embodiment of the present invention.

FIG. 7 shows a long-term unloading comparison for dental appliances, inaccordance with an embodiment of the present invention.

FIG. 8 provides a long-term movement comparison for dental appliances,in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, various embodiments of the presentinvention will be described. For purposes of explanation, specificconfigurations and details are set forth in order to provide a thoroughunderstanding of the embodiments. However, it will also be apparent toone skilled in the art that the present invention may be practicedwithout the specific details. Furthermore, well-known features may beomitted or simplified in order not to obscure the embodiment beingdescribed.

Multilayer orthodontic positioning appliances are provided, as well asrelated methods and systems. During orthodontic treatment, it may benecessary to apply forces to a tooth to generate movement of the toothto, for example, bring the patient's teeth into a better occlusion in amesial or distal direction. The presently disclosed appliances, methods,and systems provide means by which such forces can be applied duringorthodontic treatment where appliances having teeth receiving cavitiesare used, such as preformed appliances/aligners available from AlignTechnology, Inc., San Jose, Calif., under the trade name Invisalign®System. As provided by the present invention, the aligners that includemultilayer sheets can, for example, provide increased durability of thealigners so that they can better withstand wear due to alignerreinsertion and removal and other mechanical stresses put on the alignerduring treatment. In addition, the aligners have improved elasticproperties that allow for less degradation in the shape of the teethreceiving cavities during a stage of treatment. For example, during amultistage orthodontic treatment, the force exerted by an aligner toperform defined tooth movement can degrade and may cause the treatmentto include more aligners to reach a final ideal arrangement and/orresult in a mid-course correction that could be prevented by usingaligners with improved physical properties, such as those providedherein.

In one embodiment, the present invention provides a dental appliance forpositioning a patient's teeth. The dental appliance can include aremovable orthodontic tooth positioning appliance having teeth receivingcavities shaped to directly receive at least some of the patient's teethand apply a resilient positioning force to the patient's teeth, theappliance comprising a hard polymer layer disposed between a first softpolymer layer and a second soft polymer layer.

In another embodiment, the present invention provides an orthodonticsystem for positioning a patient's teeth. The orthodontic system caninclude a plurality of incremental position adjustment appliances havingteeth receiving cavities shaped to directly receive at least some of thepatient's teeth and apply a resilient positioning force to the patient'steeth, wherein the appliances are successively worn by a patient to moveteeth from one arrangement to a successive arrangement, and wherein atleast one of the appliances comprises a hard polymer layer disposedbetween a first soft polymer layer and a second soft polymer layer.

In yet another embodiment, the present invention provides a method ofmaking a dental appliance for positioning a patient's teeth. The methodcan include providing a sheet comprising a hard polymer layer ofpolymeric material disposed between a first soft polymer layer and asecond soft polymer layer, providing a positive model of the patient'steeth in a target position; and fabricating an appliance as a negativeof the positive model comprising thermoforming the sheet over thepositive model.

Referring now to the drawings, in which like reference numeralsrepresent like parts throughout the several views, FIG. 1 provides anappropriate starting point in a detailed discussion of variousembodiments of the present invention with respect to tooth repositioningappliances designed to apply repositioning forces to teeth. A toothrepositioning appliance 10 can be worn by a patient in order to achievean incremental repositioning of individual teeth in the jaw 12. Theappliance can include a shell (e.g., a polymeric shell) havingteeth-receiving cavities that receive and resiliently reposition theteeth. In many embodiments, a polymeric appliance can be formed from asheet of suitable layers of polymeric material. An appliance can fitover all teeth present in an upper or lower jaw, or less than all of theteeth. In some cases, only certain teeth received by an appliance willbe repositioned by the appliance while other teeth can provide a base oranchor region for holding the appliance in place as it applies forceagainst the tooth or teeth targeted for repositioning. In some cases,many or most, and even all, of the teeth will be repositioned at somepoint during treatment. Teeth that are moved can also serve as a base oranchor for holding the appliance as it is worn by the patient.Typically, no wires or other means will be provided for holding anappliance in place over the teeth. In some cases, however, it may bedesirable or necessary to provide individual anchors on teeth withcorresponding receptacles or apertures in the appliance so that theappliance can apply a selected force on the tooth. Exemplary appliances,including those utilized in the Invisalign® System, are described innumerous patents and patent applications assigned to Align Technology,Inc. including, for example, in U.S. Pat. Nos. 6,450,807, and 5,975,893,as well as on the company's website, which is accessible on the WorldWide Web (see, e.g., the url invisalign.com”).

An appliance can be designed and/or provided as part of a set of aplurality of appliances. In such an embodiment, each appliance may beconfigured so a tooth-receiving cavity has a geometry corresponding toan intermediate or final tooth arrangement intended for the appliance.The patient's teeth can be progressively repositioned from an initialtooth arrangement to a target tooth arrangement by placing a series ofincremental position adjustment appliances over the patient's teeth. Atarget tooth arrangement can be a planned final tooth arrangementselected for the patient's teeth at the end of all planned orthodontictreatment. Alternatively, a target arrangement can be one of manyintermediate arrangements for the patient's teeth during the course oforthodontic treatment, which may include where surgery is recommended,where inter-proximal reduction (IPR) is appropriate, where a progresscheck is scheduled, where anchor placement is best, where palatalexpansion is desirable, etc. As such, it is understood that a targettooth arrangement can be any planned resulting arrangement for thepatient's teeth that follows one or more incremental repositioningstages. Likewise, an initial tooth arrangement can be any initialarrangement for the patient's teeth that is followed by one or moreincremental repositioning stages. The adjustment appliances can begenerated all at the same stage or in sets or batches, e.g., at thebeginning of a stage of the treatment, and the patient wears eachappliance until the pressure of each appliance on the teeth can nolonger be felt or has resulted in the maximum amount of expressed toothmovement for that given stage. A plurality of different appliances(e.g., set) can be designed and even fabricated prior to the patientwearing any appliance of the plurality. After wearing an appliance foran appropriate period of time, the patient replaces the currentappliance with the next appliance in the series until no more appliancesremain. The appliances are generally not affixed to the teeth and thepatient may place and replace the appliances at any time during theprocedure (e.g., patient-removable appliances). The final appliance orseveral appliances in the series may have a geometry or geometriesselected to overcorrect the tooth arrangement, i.e., have a geometrywhich would (if fully achieved) move individual teeth beyond the tootharrangement which has been selected as the “final.” Such over-correctionmay be desirable in order to offset potential relapse after therepositioning method has been terminated, i.e., to permit movement ofindividual teeth back toward their pre-corrected positions.Over-correction may also be beneficial to speed the rate of correction,i.e., by having an appliance with a geometry that is positioned beyond adesired intermediate or final position, the individual teeth will beshifted toward the position at a greater rate. In such cases, the use ofan appliance can be terminated before the teeth reach the positionsdefined by the appliance.

In general, structures, methods and systems of the present inventionutilize a multilayer sheet for use in orthodontic appliances. Themultilayer sheet can include three layers, in which a hard polymer layeris disposed between two soft polymer layers. The multilayer sheets usedin the present invention can be used in making dental aligners havingimproved durability for use, e.g., to the elastic properties of themultilayer sheet when formed into an aligner. In addition, the bondingstrength between the layers further improves the durability of thealigners, for example, by withstanding teeth grinding by a patient.

FIG. 2 shows a multilayer structure according to the present invention.As shown, a multilayer sheet 20 can include a three layer structure: ahard polymer layer 24 and two soft polymer layers 22, 26. The hardpolymer layer can be disposed between a first soft polymer layer and asecond soft polymer layer. In some embodiments, the hard polymer layercan be thicker than either of the soft polymer layers. The soft polymerlayers can have the same or different thicknesses. For example, the hardpolymer layer can range from a thickness of about 550 μm to about 750μm. The soft polymer layers can range from a thickness of about 25 μm toabout 100 μm. Multilayer sheets used for making appliances having a hardpolymer layer disposed between two soft polymer layers can range from athickness of about 600 μm to about 1000 μm. In some embodiments, thethicknesses of the various layers can be tailored for a particular stageof treatment for the patient.

Suitable polymeric materials for the hard polymer layer can include apolyester, a co-polyester, a polycarbonate, a thermoplasticpolyurethane, a polypropylene, a polyethylene, a polypropylene andpolyethylene copolymer, an acrylic, a cyclic block copolymer, apolyetheretherketone, a polyamide, a polyethylene terephthalate, apolybutylene terephthalate, a polyetherimide, a polyethersulfone, apolytrimethylene terephthalate or a combination thereof (e.g., a blendof at least two of the listed hard polymeric materials). In someembodiments, the hard polymer layer of the appliances can includepolymeric materials, such as a polycarbonate, a co-polyester, apolyester, and a thermoplastic polyurethane. In some embodiments, thehard layer can be composed of multiple hard layers, e.g., two or threehard polymer layers 24-1, 24-2, 24-N co-extruded to form one hard layer.

The hard polymer layer of the appliances of the present invention canhave a variety of physical properties that can, e.g., improve treatmentoptions for a practitioner. For example, physical properties such astensile strength, elongation at yield, elongation at break, tensilemodulus, flexural modulus, stress relaxation over time, and lighttransmission can each be specifically tailored for a particularapplication. In some embodiments, the hard polymer layer of theappliances can have a physical property of at least one of a tensilestrength at yield of between about 4000 pounds per square inch (psi) and6500 psi, an elongation at yield of greater than about 4%, an elongationat break of greater than about 70%, a tensile modulus of greater thanabout 150,000 psi, a flexural modulus greater than about 150,000 psi, astress relaxation at 24 hours testing in a wet environment (e.g.,between about 90%-100% relative humidity) is greater than 10%, and alight transmission between 400 nm and 800 nm of greater than about 75%.

Suitable polymeric materials for the soft polymer layers of theappliance can include a styrenic block copolymer (SBC), a siliconerubber, an elastomeric alloy, a thermoplastic elastomer (TPE), athermoplastic vulcanizate (TPV) elastomer, a polyurethane elastomer, ablock copolymer elastomer, a polyolefin blend elastomer, a thermoplasticco-polyester elastomer, a thermoplastic polyamide elastomer, or acombination thereof (e.g., a blend of at least two of the listed softpolymeric materials). The soft polymer layers can be the same materialor a different material. In certain embodiments, the first soft polymerlayer and the second soft polymer layer are the same polymeric material.

The soft polymer layers of the appliances can have a variety of physicalproperties. For example, physical properties such as hardness, ultimatetensile strength, elongation at break, tensile modulus, compression set,flexural modulus, and light transmission can each be specificallytailored for a particular application. In some embodiments, the softpolymer layers of the appliances can independently have a physicalproperty of at least one of a hardness of about 60A to about 85D, anultimate tensile strength of greater than about 5000 psi, an elongationat break of greater than about 200%, a compression set at about 70° C.of greater than 40% after 24 hours, a flexural modulus of greater thanabout 35,000 psi, and a light transmission between 400 nm and 800 nm ofgreater than about 75%.

As described herein, the layers of the appliances can include a hardpolymer layer disposed between two soft polymer layers. In oneembodiment, the multilayer appliances can include a hard polymer layerof one type of material (e.g., a co-polyester), and two soft polymerlayers of other types of material that can be the same or different(e.g., two soft polymer layers of thermoplastic polyurethane elastomer).In some embodiments, the multilayer appliances can also include a hardpolymer layer of at least two layers of polymer material. For example,the hard polymer layer can include several polymer layers laminatedtogether to form the hard polymer layer. The laminated hard polymerlayer can include at least two layers of any combination of thefollowing polymer materials: a polyester, a co-polyester, apolycarbonate, a thermoplastic polyurethane, a polypropylene, apolyethylene, a polypropylene and polyethylene copolymer, an acrylic, acyclic block copolymer, a polyetheretherketone, a polyamide, apolyethylene terephthalate, a polybutylene terephthalate, apolyetherimide, a polyethersulfone, and a polytrimethyleneterephthalate. Similarly, in some embodiments, the multilayer appliancescan include a soft polymer layer of at least two layers of polymermaterial. For example, the soft polymer layers 22, 26 can include alayer of several polymer layers 22-1, 22-2, 22-N and 26-1, 26-2, 26-N,respectively, laminated together. The laminated soft polymer layers caninclude at least two layers of any combination of the following polymermaterials: a styrenic block copolymer (SBC), a silicone rubber, anelastomeric alloy, a thermoplastic elastomer (TPE), a thermoplasticvulcanizate (TPV) elastomer, a polyurethane elastomer, a block copolymerelastomer, a polyolefin blend elastomer, a thermoplastic co-polyesterelastomer, and a thermoplastic polyamide elastomer.

The tooth positioning appliances can be fabricated using a variety ofmethods. For example, methods for making the appliances can includethermoforming a multilayer sheet into an aligner by heating the sheetand then molding the sheet to a particular configuration. Exemplarymethods for fabricating the appliances, including those utilized in theInvisalign® System, are described in numerous patents and patentapplications assigned to Align Technology, Inc. including, for example,in U.S. application Ser. No. 13/186,374 as well as on the company'swebsite, which is accessible on the World Wide Web (see, e.g., the urlinvisalign.com”).

FIG. 3 depicts an example embodiment of a process 30 for forming amultilayer tooth positioning appliance, in accordance with an embodimentof the present invention. As shown, a multilayer sheet 32 can be formedinto a tooth positioning appliance 36. The multilayer sheet 32, asdepicted, can include three layers: a hard polymer layer disposedbetween two soft polymer layers. In this example process, the toothpositioning appliance 36 can be produced with the use of a physicaltooth model, or mold, 34. The tooth positioning appliance 36 can beproduced by heating the thermoformable multilayer sheet 32 and thenvacuum or pressure forming the sheet over the teeth in the physicaltooth model 34. The tooth positioning appliance 36 is a directrepresentation of the physical tooth model. Excess material from thesheet can be trimmed to form a final tooth positioning appliance thatcan be used for orthodontic treatment of a patient.

One or a series of physical tooth models, such as the model describedabove, may be used in the generation of elastic repositioning appliancesfor orthodontic treatment. Similar to the process above, each of theappliances can be generated by thermoforming a multilayer polymericmaterial over a mold of a desired tooth arrangement to form a dentalappliance. The tooth positioning appliance of the desired tootharrangement generally conforms to a patient's teeth but is slightly outof alignment with the initial tooth configuration. Placement of theelastic positioner over the teeth applies controlled forces in specificlocations to gradually move the teeth into the desired configuration.Repetition of this process with successive appliances comprising newconfigurations eventually moves the teeth through a series ofintermediate configurations to a final desired configuration.

The present invention includes a variety of methods for fabricatingdental appliances. FIG. 4 shows a simple schematic for a method 40 offabricating a removable orthodontic tooth positioning appliance havingteeth receiving cavities shaped to directly receive at least some of thepatient's teeth and apply a resilient positioning force to the patient'steeth, in accordance with an embodiment of the present invention. Themethod can include providing a multilayer sheet having a hard polymerlayer disposed between two soft polymer layers (Step 42). The method canfurther include providing a positive physical model of a patient's teeth(Step 44). The tooth positioning appliance can be fabricated bythermoforming the multilayer sheet over the positive physical model(Step 46), in which the tooth positioning appliance is a negative of thepositive model. As described above, the methods of fabrication canfurther include trimming or cutting portions of the sheet to render afinal, usable appliance for orthodontic treatment.

Multilayer sheets of the present invention were analyzed and determinedto provide a variety of improved properties for aligners used inorthodontic treatment. As further described herein, the multilayersheets formed into aligners can, for example, provide increaseddurability of the aligners so that they can better withstand wear due toteeth grinding and other mechanical stresses put on the aligner duringtreatment. In addition, the aligners have improved elastic propertiesthat allow for less degradation in the shape of the teeth receivingcavities during a stage of treatment. For example, during a multistageorthodontic treatment, the capability of an aligner to force toothmovement can degrade and may cause the treatment to include morealigners to reach a final ideal arrangement and/or result in amid-course correction that could be prevented by using aligners withimproved physical properties, such as those provided herein.

FIGS. 5-8 provide example test results that compare various physicalproperties of the multilayer sheet appliances of the present inventionwith other already existing aligner materials (Material 1). Samples ofvaried thicknesses were tested. For example, multilayer sheets weretested having a hard polymer layer with thicknesses ranging from about580 μm to about 715 μm thick. In some examples, the hard layer was aco-polyester hard polymer layer. The soft layers tested ranged betweenabout 50 μm to about 100 μm. In some examples, the hard polymer layerwas disposed between thermoplastic polyurethane elastomer soft polymerlayers. As shown in FIGS. 5 and 6, one example of the multilayer sheetmaterial (Material 2) showed improved stress relaxation properties ascompared to another already existing material (Material 1) at roomtemperature and 37° C. In addition, FIG. 7 shows improved long-termunloading characteristics of the multilayer sheet Material 2 versus thealready existing Material 1. The multilayer sheet showed less deflectionunder force loads. FIG. 8 also shows improved long-term movement datafor the multilayer sheet Material 2 versus Material 1.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing embodiments (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. The term “connected” is to beconstrued as partly or wholly contained within, attached to, or joinedtogether, even if there is something intervening. Recitation of rangesof values herein are merely intended to serve as a shorthand method ofreferring individually to each separate value falling within the range,unless otherwise indicated herein, and each separate value isincorporated into the specification as if it were individually recitedherein. All methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein, is intended merely to betterilluminate embodiments and does not pose a limitation on the scopeunless otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element as essential to thepractice of at least one embodiment.

Variations of the embodiments described herein may become apparent tothose of ordinary skill in the art upon reading the foregoingdescription. The inventors expect skilled artisans to employ suchvariations as appropriate, and the inventors intend for embodiments tobe constructed otherwise than as specifically described herein.Accordingly, suitable embodiments include all modifications andequivalents of the subject matter recited in the claims appended heretoas permitted by applicable law. Moreover, any combination of theabove-described elements in all possible variations thereof iscontemplated as being incorporated into some suitable embodiment unlessotherwise indicated herein or otherwise clearly contradicted by context.The scope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the pending claims along with their full scope orequivalents.

What is claimed is:
 1. A multilayer dental appliance comprising teethreceiving cavities shaped to directly receive at least some of apatient's teeth and apply a resilient positioning force to the patient'steeth, the appliance comprising: a soft polymer layer comprising a softpolymeric material having an ultimate tensile strength of greater thanabout 5000 psi, an elongation at break of greater than about 200%, and ahardness of about 60 A to about 85 D; and a hard polymer layercomprising a co-polyester.
 2. The multilayer dental appliance of claim1, wherein the hard polymer layer comprises a hard polymer layer elasticmodulus and the soft polymer layer comprises a soft polymer layerelastic modulus less than the hard polymer layer elastic modulus.
 3. Themultilayer dental appliance of claim 1, wherein the soft polymer layercomprises a thermoplastic polyurethane elastomer.
 4. The multilayerdental appliance of claim 1, wherein the soft polymer layer comprisesone or more of: a flexural modulus of greater than about 35,000 psi, acompression set greater than 40% after 24 hours at 70° C., or a lighttransmission between 400 nm and 800 nm of greater than about 75%.
 5. Themultilayer dental appliance of claim 1, wherein the hard polymer layercomprises a tensile modulus greater than 150,000 psi, a tensile strengthat yield between 4000 psi and 6500 psi, or a combination thereof.
 6. Themultilayer dental appliance of claim 1, wherein the soft polymericmaterial comprises a material selected from the group consisting of: athermoplastic polyurethane elastomer, a silicone rubber, an elastomericalloy, a thermoplastic elastomer (TPE), a thermoplastic vulcanizate(TPV) elastomer, a block copolymer elastomer, a polyolefin blendelastomer, a thermoplastic co-polyester elastomer, and a thermoplasticpolyamide elastomer, or a combination thereof.
 7. The multilayer dentalappliance of claim 1, wherein the soft polymeric material comprises ablend of polymeric materials, including two or more materials selectedfrom the group consisting of: a thermoplastic polyurethane elastomer, asilicone rubber, an elastomeric alloy, a thermoplastic elastomer (TPE),a thermoplastic vulcanizate (TPV) elastomer, a block copolymerelastomer, a polyolefin blend elastomer, a thermoplastic co-polyesterelastomer, and a thermoplastic polyamide elastomer.
 8. The multilayerdental appliance of claim 1, comprising three or more polymer layers. 9.The multilayer dental appliance of claim 1, wherein the hard polymerlayer comprises a blend of polymeric materials including theco-polyester and one or more of: a polyester, a thermoplasticpolyurethane, a polypropylene, a polyethylene, a polypropylene andpolyethylene copolymer, an acrylic, a polyetheretherketone, a polyamide,a polyethylene terephthalate, a polybutylene terephthalate, apolyetherimide, a cyclic block copolymer, a polyethersulfone, apolytrimethylene terephthalate, or a combination thereof.
 10. Themultilayer dental appliance of claim 1, wherein the hard polymer layercomprises at least two layers including a first layer comprising theco-polyester and a second layer comprising one or more of: a polyester,a co-polyester, a thermoplastic polyurethane, a polypropylene, apolyethylene, a polypropylene and polyethylene copolymer, an acrylic, apolyetheretherketone, a polyamide, a polyethylene terephthalate, apolybutylene terephthalate, a polyetherimide, a cyclic block copolymer,a polyethersulfone, or a polytrimethylene terephthalate.
 11. Themultilayer dental appliance of claim 1 comprising a thickness of between500 μm and 1200 μm.
 12. The multilayer dental appliance of claim 1,wherein the hard polymer layer comprises at least one of: an elongationat yield of greater than about 4%, an elongation at break of greaterthan about 70%, a flexural modulus greater than about 150,000 psi, astress relaxation of greater than about 10% at 24 hours testing in ahigh humidity environment, or a light transmission between 400 nm and800 nm of greater than about 75%.
 13. A plurality of incrementalposition adjustment appliances having teeth receiving cavities shaped todirectly receive at least some of a patient's teeth and apply aresilient positioning force to the patient's teeth, wherein theappliances are shaped to move teeth from one arrangement to a successivearrangement when successively worn by the patient, and wherein at leastone of the appliances comprises: a soft polymer layer comprising a softpolymeric material having an ultimate tensile strength of greater thanabout 5000 psi, an elongation at break of greater than about 200%, and ahardness of about 60 A to about 85 D; and a hard polymer layercomprising a co-polyester.
 14. The plurality of incremental positionadjustment appliances of claim 13, wherein the hard polymer layercomprises a hard polymer layer elastic modulus and the soft polymerlayer comprises a soft polymer layer elastic modulus less than the hardpolymer layer elastic modulus.
 15. The plurality of incremental positionadjustment appliances of claim 13, wherein the soft polymer layercomprises a thermoplastic polyurethane elastomer.
 16. The plurality ofincremental position adjustment appliances of claim 13, wherein the softpolymer layer comprises one or more of: a flexural modulus of greaterthan about 35,000 psi, a compression set greater than 40% after 24 hoursat 70° C., or a light transmission between 400 nm and 800 nm of greaterthan about 75%.
 17. The plurality of incremental position adjustmentappliances of claim 13, wherein the hard polymer layer comprises atensile modulus greater than 150,000 psi, a tensile strength at yieldbetween 4000 psi and 6500 psi, or a combination thereof.
 18. Theplurality of incremental position adjustment appliances of claim 13,wherein the soft polymeric material comprises a material selected fromthe group consisting of: a thermoplastic polyurethane elastomer, asilicone rubber, an elastomeric alloy, a thermoplastic elastomer (TPE),a thermoplastic vulcanizate (TPV) elastomer, a block copolymerelastomer, a polyolefin blend elastomer, a thermoplastic co-polyesterelastomer, and a thermoplastic polyamide elastomer, or a combinationthereof.
 19. The plurality of incremental position adjustment appliancesof claim 13, wherein at least one of the appliances comprises three ormore polymer layers.
 20. A method of moving a patient's teeth from aninitial configuration towards a target configuration, the methodcomprising: providing a removable orthodontic tooth positioningappliance having teeth receiving cavities shaped to directly receive atleast some of a patient's teeth; and placing the removable orthodontictooth positioning appliance on the teeth of the patient to apply aresilient positioning force to the patient's teeth and thereby move theteeth towards the target configuration, wherein the appliance comprises:a soft polymer layer comprising a soft polymeric material having anultimate tensile strength of greater than about 5000 psi, an elongationat break of greater than about 200%, and a hardness of about 60 A toabout 85 D; and a hard polymer layer comprising a co-polyester.
 21. Themethod of claim 20, wherein providing the removable orthodontic toothpositioning appliance comprises providing a series of incrementalposition adjustment appliances, said series of incremental positionadjustment appliances including the removable orthodontic toothpositioning appliance.
 22. The method of claim 20, wherein providing theseries of incremental position adjustment appliances comprises placingsaid series of incremental position adjustment appliances over thepatient's teeth.
 23. The method of claim 20, wherein the soft polymerlayer comprises one or more of: a flexural modulus of greater than about35,000 psi, a compression set greater than 40% after 24 hours at 70° C.,or a light transmission between 400 nm and 800 nm of greater than about75%.
 24. The method of claim 20, wherein the hard polymer layercomprises one or more of: a tensile modulus greater than 150,000 psi, atensile strength at yield between 4000 psi and 6500 psi, an elongationat yield of greater than about 4%, an elongation at break of greaterthan about 70%, a flexural modulus greater than about 150,000 psi, astress relaxation of greater than about 10% at 24 hours testing in ahigh humidity environment, or a light transmission between 400 nm and800 nm of greater than about 75%.
 25. The method of claim 20, furthercomprising fabricating the removable orthodontic tooth positioningappliance.
 26. The method of claim 20, wherein the hard polymer layercomprises a hard polymer layer elastic modulus and the soft polymerlayer comprises a soft polymer layer elastic modulus less than the hardpolymer layer elastic modulus.
 27. The method of claim 20, wherein thesoft polymer layer comprises a thermoplastic polyurethane elastomer. 28.The method of claim 20, wherein the soft polymeric material comprises amaterial selected from the group consisting of: a thermoplasticpolyurethane elastomer, a silicone rubber, an elastomeric alloy, athermoplastic elastomer (TPE), a thermoplastic vulcanizate (TPV)elastomer, a block copolymer elastomer, a polyolefin blend elastomer, athermoplastic co-polyester elastomer, and a thermoplastic polyamideelastomer, or a combination thereof.
 29. The method of claim 20, whereinthe appliance comprises three or more polymer layers.
 30. The method ofclaim 20, wherein the appliance comprises a thickness of between 500 μmand 1200 μm.